1. Field of the Invention
This invention relates in general to oil well sucker rods. In particular, the invention relates to oil well sucker rods made of fiberglass with steel connectors on each end.
2. Description of the Prior Art
In many oil wells the pressure in the oil reservoir is insufficient to lift the oil to the surface. In such cases it is conventional to use a sub-surface pump to force the oil out of the well. The sub-surface pump is driven by a pumping unit located at the surface.
The pumping unit is connected to the sub-surface pump by a string of sucker rods. The pumping unit moves the sucker rod string up and down to drive the sub-surface pump.
For many years sucker rods were generally made of steel. Due to the heavy weight of the steel sucker rods, large pumping units were required and pumping depths were limited. It is now preferable to use sucker rods made of fiberglass with steel connectors. Fiberglass rods provide sufficient strength and yet weigh substantially less than steel rods.
Since the invention of the fiberglass sucker rod, efforts have continued to improve the steel connectors between successive rods. For example, U.S. Pat. No. 4,653,953, issued Mar. 31, 1987, to Anderson et al., shows a fiberglass sucker rod having a typical prior art connector.
The connector shown in Anderson et al. has a rod-receiving receptacle and a plurality of axially spaced, annular, tapered surfaces. Bonding material between the rod and the connector holds the rod within the receptacle. The tapered surfaces create increased compressive forces to significantly improve the grip of the bonding agent on the rod. The taper angles of the tapered surfaces are progressively smaller toward the open end of the receptacle.
U.S. Pat. No. 4,401,396, issued Aug. 30, 1983, to McKay, shows another typical sucker rod. The rod is centered within the receptacle of the connector by a centering ring and by the tapered end of the rod. Other sucker rod connectors have used evenly spaced dimples to center the rod within the receptacle.
U.S. Pat. No. Re. 32,865, issued Feb. 14, 1989, to Rutledge, Jr. et al., discloses another typical sucker rod. The outer surface of the connector is generally cylindrical. However, the outer surface of the connector is tapered adjacent to the internal tapered surface nearest the open end of the receptacle.